Good Perpendicular Magnetic Anisotropy Research Articles

The Success of Fabrication of Pure SmFe2 Phase Film with Outstanding Perpendicular Magnetic Anisotropy.

This study used DC magnetron sputtering technology to fabricate Sm-Fe films and systematically investigated the phase transition behavior of Sm-Fe films with different Fe ratios. It was found that at higher Fe content, the films consisted of Sm2Fe17 or SmFe7 phases; as Fe content decreased, the films were mainly composed of SmFe3 or SmFe2 phases; at higher Sm content, the films primarily consisted of Sm phase. Sm is prone to volatilization at high temperatures, so Ta was used as a capping layer to effectively suppress Sm volatilization, successfully synthesizing pure SmFe2 phase films at a nearly 1:2 ratio. The magnetic properties and magnetostrictive behavior of the SmFe2 films were investigated, revealing that pure-phase SmFe2 films exhibit good perpendicular magnetic anisotropy and magnetostriction properties. The larger stress along the perpendicular-to-film direction, resulting from the absence of substrate-induced constraints, contributes to the excellent perpendicular magnetic anisotropy of the films. This study successfully synthesized pure-phase SmFe2 films and discovered a new method for fabricating perpendicularly anisotropic films. The research findings are of great significance for the efficient synthesis of desired films with high phase formation temperatures containing volatile elements.

Current-induced magnetization switching in a chemically disordered A1 CoPt single layer

We report the first demonstration of current-induced magnetization switching in a perpendicularly magnetized A1 CoPt single layer. We show that good perpendicular magnetic anisotropy can be obtained over a wide composition range of A1 Co1−xPtx single layers, which allows the fabrication of a perpendicularly magnetized CoPt single layer with a composition gradient that breaks the inversion symmetry of the structure. By fabricating a CoPt single layer with a gradient, we were able to evaluate spin-orbit torque (SOT) efficiency and successfully realize SOT-induced magnetization switching. Our study provides an approach for realizing current-induced magnetization in ferromagnetic single layers without attaching SOT source materials.

Perpendicular Magnetic Anisotropy Study of Co/Pt Multilayers

The perpendicular magnetic anisotropy (PMA) of Pt(t1Pt)/[Co(tCo)/Pt(t2Pt)]n which prepared by magnetron sputtering technique was studied in this article. The impact to PMA and magnetic properties of Co/Pt multilayers was investigated from the aspects of Co layer thicknesses tCo, Pt inner layer thicknesses t2Pt, Pt underlayer thicknesses t1Pt and periodic number n. The test results show that interfacial effects are the main factors which influence the PMA and other macroscopic properties of the samples. From comparison of the test results of magnetic properties the best multilayer structure Pt 1.0 nm/(Co 0.4 nm/Pt 0.8 nm)3 was obtained. Anisotropic energy of the best sample was 2.0 × 105 J.m−3 which indicated that it has good perpendicular magnetic anisotropy.

Effect of buffer and interlayer on the adhesion and magnetic properties of anisotropic Nd–Fe–B single and multilayer films

Nd–Fe–B films with good perpendicular magnetic anisotropy were obtained by using a Mo film with the thickness of about 40nm as buffer layer. Large out-of-plane coercivity (Hc⊥=1182kA/m) and remanent ratio (remanent magnetization/saturation magnetization)⊥=0.99 are obtained by the stratification of the Nd–Fe–B magnetic film in three NdFeB(180nm)/Mo(5nm) bilayer sequences using Mo as interlayer. Using a Ni film, with a thickness of about 8nm, alongside with a Mo film of 40nm as buffer layer improves the adhesion to substrate and keeps the anisotropic hard magnetic performances of the Nd–Fe–B films unchanged. By increasing the total thickness of the Nd–Fe–B magnetic layer from 540nm to 1620nm the coercivity measured at high fields increases from about 1350kA/m for Nd–Fe–B film with 3 NdFeB(180nm)/Mo(5nm) sequences to about 1640kA/m for Nd–Fe–B film with 9 NdFeB(180nm)/Mo(5nm) sequences which can be ascribed to a stronger pinning effect as a result of the increased number of NdFeB/Mo interfaces.

Perpendicular magnetic anisotropy in Ta|Co40Fe40B20|MgAl2O4 structures and perpendicular CoFeB|MgAl2O4|CoFeB magnetic tunnel junction

Magnetic properties of Co40Fe40B20 (CoFeB) thin films sandwiched between Ta and MgAl2O4 layers have been systematically studied. For as-grown state, Ta/CoFeB/MgAl2O4 structures exhibit good perpendicular magnetic anisotropy (PMA) with interface anisotropy Ki = 1.22 erg/cm2, which further increases to 1.30 erg/cm2 after annealing, while MgAl2O4/CoFeB/Ta multilayer shows in-plane magnetic anisotropy and must be annealed in order to achieve PMA. For bottom CoFeB layer, the thickness window for PMA is from 0.6 to 1.0 nm, while that for top CoFeB layer is between 0.8 and 1.4 nm. Perpendicular magnetic tunnel junctions (p-MTJs) with a core structure of CoFeB/MgAl2O4/CoFeB have also been fabricated and tunneling magnetoresistance ratio of about 36% at room temperature and 63% at low temperature have been obtained. The intrinsic excitations in the p-MTJs have been identified by inelastic electron-tunneling spectroscopy.

Microstructures and Magnetic Properties of FePt Thin Films on TiON Intermediate Layer

The microstructures and magnetic properties of FePt(-SiOx-C) thin films grown on TiON and TiON/TiN intermediate layers were studied. TiON possessed smaller surface energy and smaller lattice constant than TiN. With increasing TiOx doping concentration, FePt grain shape changed from semi-spherical to square and grain size was significantly reduced. Meanwhile, good perpendicular magnetic anisotropy was retained, indicating that TiON intermediate layer could achieve a good balance between island growth and epitaxial growth. Furthermore, using TiON/TiN combined intermediate layer, FePt grain size was further reduced and the opening-up of in-plane M-H loop diminished. With 45 vol.% SiOx-25 vol.% C doping, well-isolated FePt grains with an average size as small as 5.7 nm and the grain size distribution of 0.9 nm were achieved. It also exhibited good perpendicular magnetic anisotropy with an out-of-plane coercivity of 18 kOe.

Enhance the coercivity of the rhombohedral lattice L11 CoPt thin film on glass substrate

CoPt L11 thin films with different thicknesses of 2-50 nm were epitaxially grown on Pt(111) underlayer on amorphous glass substrates by magnetron sputtering. The results show that high out-of-plane coercivity (Hc⊥), good perpendicular magnetic anisotropy (PMA), large magnetocrystalline anisotropy constant (Ku), and negative nucleation field (Hn) were achieved simultaneously in the thinner CoPt films, indicating a high impedance in the domain wall motion. TEM cross-section images displayed a well developed epitaxy of CoPt L11(111) orientation starting from Pt(111) plane and extending into magnetic CoPt(111) film, inducing the PMA of CoPt films. Surface morphologies of CoPt/Pt/glass films confirmed that surface CoPt grain sizes are similar to their magnetic domain sizes found in magnetic force microscopy results, evidencing the grain boundary pinning effect on the enhancement of Hc⊥. When the thickness of CoPt film was reduced to 3 nm, higher PMA with Hc⊥ ∼ 1.8 kOe and Ku ∼ 1.9 × 107 erg/cm3 suggests that L11 CoPt thin film is a promising candidate in the design of advanced spintronic devices, magnetic sensors, and magnetic recording media.

Study of low-temperature ordering and crystal structure in FePtBi/Au nanocomposite films

Based on interfacial microstructure control of FePt/Au multilayer structure and surfactant Bi atoms, an FePtBi/Au nanocomposite film was designed to achieve good properties [low-temperature ordering, good perpendicular magnetic anisotropy (PMA), and no interparticle exchange coupling (IEC)] in this paper. The ordering process was promoted due to the increase of concentration of defects by adding appropriate surfactant Bi atoms. Thus, the ordering temperature of this film can be decreased from 500 to 450 °C. Meantime, the FePtBi/Au nanocomposite film maintains good PMA and low IEC with the texture manipulation of Au layers and control of total film thickness.

High perpendicular hard magnetic properties of nanocomposite Co-rich Co–Pt/Pt double-layered films by epitaxial deposition without capped layer

The HRTEM cross-sectional lattice image shows that a well epitaxial growth of hcp Co-rich Co–Pt (002) on Pt (111) underlayer leads to good perpendicular magnetic anisotropy of Co-rich Co–Pt film. It is found that both the perpendicular coercivity ( Hc ⊥) and perpendicular squareness ( S ⊥) of Co-rich Co–Pt films without Pt capped layer are larger than that of Co-rich Co–Pt films with Pt capped layer. The cross-sectional TEM-EDS and AES analysis confirm that the oxygen atoms will diffuse from film surface into the Co-rich Co–Pt film without adding Pt capped layer, and it react with cobalt atoms to form CoO, which is detected by XPS analysis. The increase in perpendicular hard magnetic properties of Co-rich Co–Pt film without Pt capped layer is mainly due to form CoO in the Co-rich Co–Pt film.

Reduction of grain size and exchange coupling strength of Nd2Fe14B thin films by Al addition

NdFeB thin films of good perpendicular magnetic anisotropy have been successfully deposited on W underlayer by DC magnetron sputtering. Cu and Al elements are introduced to improve the structural and magnetic properties of the NdFeB films. The deposition temperature is lowered to 400 °C by the addition of 1.0 at.% Cu. The average grain size is reduced to 10 nm by the introduction of 10.0 at.% Al. With the reduction of the grain size, the exchange coupling interaction between the grains is weakened. The magnetization reversal process of the grains directly depends on the grain size and shape. Before Al addition, most of the grains are demagnetized by magnetization incoherent rotation but in the film doped with 5.0 at.% Al, the magnetization is coherently reversed, as demonstrated by the comparison of the physical grain volume and the thermal switching volume. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Magnetic and microstructural properties of hard magnetic NdFeB films prepared on a Ta buffer by pulsed laser deposition

Hard magnetic NdFeB films were prepared by pulsed laser deposition at different substrate temperatures on a Ta buffer. With increasing deposition temperature, the in-plane to out-of-plane remanence ratio decreases to less than 0.1, indicating a very good perpendicular magnetic anisotropy. However, for temperatures above 600/spl deg/C the increasing grain size reduces coercivity. A reduction in film thickness reduces grain size and increases the coercivity up to 1.5 T while maintaining a good magnetic texture.

Magnetic and magneto-optical properties of CoPtM (M = Re, Ru) alloy films for a new magneto-optical recording material

CoPtM (M = Re, Ru) ternary alloy films have been investigated as new magneto-optical materials for blue laser recording. The CoPtRe and CoPtRu alloy films were prepared by sputtering without a heating process, and exhibited good perpendicular magnetic anisotropy and magnetic hysteresis loop squareness. For the magneto-optical properties, the figure of merit for the CoPtRe alloy film with less than 15 at% Re at λ < 530nm is shown to be superior to that for TbFeCo amorphous film and inferior 0–4 dB to that of Co/Pt multilayers.

A transition-metal–rare-earth alloy for perpendicular magnetic recording

Several Co-based media have been recognized to be convenient for perpendicular magnetic recording. These alloys present a good perpendicular magnetic anisotropy and high saturation magnetization, but high demagnetizing fields and a poor perpendicular hysteresis loop squareness σ⊥. This paper describes the conditions of deposition, magnetic properties, and recording tests results obtained with radio-frequence diode-sputtered FeTbGd thin films. Near to the compensation composition, the saturation magnetization and demagnetizing fields are low and σ⊥ is nearly 1. A SiO2 protective layer covered medium has been tested for magnetic recording with a conventional Winchester ferrite head. In these recording conditions, a density as high as 162 kiloflux changes per inch has been obtained. Such results show that transition-metal–rare-earth (TM-RE) alloys are suitable for perpendicular magnetic recording.